1. Field of the Invention
This invention relates to structures used to join together two sections which together comprise a completed length pole. More particularly, the present invention is directed to structures formed on the ends of two pole member sections to allow the sections to be securely and permanently joined together without the need for fastening devices.
2. The Background of the Invention
It is common in many aspects of everyday life and commerce to require the joining of two pole-like members of some kind. Applications for such members may include light poles, flag poles, sporting equipment standards such as those used to support volleyball and badminton nets, basketball goal standards, tent poles, scaffolding supports, and a multitude of other types of poles and supports.
It is often the case that the original length of a pole is so great that it cannot be transported and stored conveniently. For example, pole supports used for backpacking tents must be broken down to several shorter sections for transportation and then reassembled prior to use.
Another example are basketball goal standards which are often shipped in lengths of only three to five feet and which must be assembled and embedded into several feet of earth to provide an upright which is between eight and ten feet high. Other examples of poles which may need to be stored and shipped in several short sections and assembled on site include flag poles and canopy supports.
Importantly, it is usually the case that pole supports for backpacking tents and the like must be capable of seizure free assembly and disassembly. That is, the joint must be easy to assemble and disassemble but yet also remain secure enough to resist inadvertent disassembly. In contrast, pole members used to construct basketball standards are generally intended to be permanently assembled and, once assembled, not disassembled. Both types of applications have particular problems which prior art devices have not adequately solved.
Pole members used in the described applications may be of a uniform outer and inner diameter along their entire length. Alternatively, the sections to be joined may be of different diameters. As used herein, the phrase "pole member" is intended to include any elongated pole-like member which must be joined to another pole-like member in order to increase the overall length of the assembled pole.
One prior art method of joining two pole sections is shown in FIG. 1. While the structure shown in FIG. 1 may be commonly used to join two pole sections such as a basketball goal standard, it suffers from several serious drawbacks as explained below.
First, due to imprecise formation of the joint, the upper pole member 10 is allowed to rock back and forth. Furthermore, as lateral forces are applied to the sections, in the direction of arrow L, the circumference of the lower end of the upper section 10 begins to flare in the direction indicated at arrows F in FIG. 1. Also, the upper end of the lower section 18 becomes narrowed in the direction indicated at arrows N in FIG. 1. The resulting flaring and narrowing, which accelerates as the pole is used more rigorously, causes the joint to loosen so that the joint is no longer able to keep the poles in lateral alignment, i.e., the pole tilts and wobbles. This problem is particularly severe when relatively thin walled tubing is used. Thus, in most cases, the upper pole section 10 wobbles back and forth in a very unsatisfactory manner even before the pole has been subjected to any use and wear.
Second, single reduced diameter segment 16 of the pole joint represented in FIG. 1 is generally formed by swaging one end of the lower section. But it is common for the diameter and wall thickness of the pole material to vary. Variations in diameter and wall thickness of the upper pole member 10 can cause a joint which is impossible to assemble or which is very unstable if the variations exceed very small values.
Third, it is common to form tubular pole members by rolling a tube from flat sheet of material and butt welding the resulting seam. When using tubular pole sections formed in this way, the seam of the pole member often protrudes from the surface of the section. When a protruding weld seam is encountered by a structure such as shown in FIG. 1, at best, an unstable joint is the result, and in the worst case, the upper and lower pole members will not fit together. Fourth, when pole sections are formed, burrs are often left where the section was cut. Such burrs once again can cause an unstable joint when the structure represented in FIG. 1 is used.
In an effort to overcome the drawbacks mentioned above, prior art solutions have required the use of bolts 12 and nuts 13 or other fasteners and pre-drilled holes 14 to secure the upper and lower sections together. The use of bolts, screws, or other fasteners, however, adds cost to the joint, inconvenience to the user, requires tools for assembly and disassembly, and often compounds problems due to flaring as indicated at arrow F in FIG. 1 since the lower end of the upper pole member 10 no longer has a perimeter contact with the tapered segment 18. Moreover, screws present at such a joint are aesthetically unsightly, and make an unsafe joint with sharp protrusions as well as requiring occasional retightening as the screws loosen.
Due to the inherent instability of such joints, manufacturers often attempt to fabricate such joints to tight tolerances which results in greater expense and a joint which is often difficult to assemble and still does not overcome the above described problems.
Another prior art structure requires that the lower pole section be provided with a long upwardly directed, continuous male taper which ends with a diameter much smaller than the original diameter of the pole. In such an arrangement, the upper pole section is provided with a correspondingly long female taper. Such long continuous tapers, however, are difficult and expensive to form and tend to more or less suffer from the same drawbacks as the joint illustrated in FIG. 1 depending upon the dimensions of the joint and the intended application of the joint.
Moreover, many of the prior art joints are often not intended to be used as a permanent joint but are specifically designed to be "seizure free," i.e., relatively easy to disassemble. Such joints generally perform inadequately either as a permanent joint or as a joint which merely resists inadvertent disassembly. A still further difficulty present in the prior art is that the structures which have been used to form joints on thin wall steel tubing have not recognized the particular problems which must be dealt with when dealing with thin walled tubing.
In view of the drawbacks and disadvantages found in the prior art, it would be an advance in the art to provide a pole joint structure which is secure and resists wear and loosening under long and heavy use. It would also be an advance in the art to provide a pole joint structure which may be assembled without the need for any tools or fasteners.
It would be a further advance in the art to provide a pole joint structure which alleviates problems with varying wall thickness, seam weld variations, and other manufacturing imperfections as well as being simple and inexpensive to form on a variety of pole section ends. It would also be an advance in the art to provide a pole joint structure which forms a permanent joint between two pole members. It would be a still further advance in the art to provide a pole joint structure particularly suited for use with thin wall steel tubing.